The invention relates to an ion flow electrostatic recording process and apparatus which utilizes an ion flow record head and electrostatic recording paper, and more particularly, to such process and apparatus in which a corona ion flow is controlled by a recording signal voltage to form an image of electrostatic charge on a dielectric record layer.
A recording process in which a record medium comprises a dielectric layer on the surface of a conductive member and an image of electrostatic charge is formed on the surface of the dielectric layer in a pattern corresponding to a record signal and then developed with toner to provide a visual image is referred to as an electrostatic recording process. Such electrostatic recording process is generally classified in one of two major categories; the use of a stylus electrode, commonly referred to as "multi-stylus" which is impressed against a dielectric layer while a high voltage record signal is applied thereto, to thereby form an electrostatic latent image on the surface of the dielectric layer, and the use of a record head comprising a source of corona ions and an element which controls a flow of corona ions produced individually for each picture element, the record head of the latter type being slightly spaced from the dielectric layer to thereby form an image of electrostatic charge on the surface of the dielectric layer in a non-contact manner.
In the former process, the record head used is simple in construction, and a drive circuit is also simple. However, it suffers from unfavorable phenomena that a record may be missed or that an abnormal record may be formed as a result of an abnormal discharge. By contrast, in the latter process which is referred to as an ion flow electrostatic recording process, the reproducibility of record dots and the uniformity of charge distribution within a dot are improved, and this process does not require any delicate contact between the dielectric layer and the record head. However, the record head used is complex in construction, and the process requires several high voltage supplies and also requires that a gap of a constant magnitude be maintained between the record head and the dielectric layer with a high accuracy.
By way of example, FIG. 19 schematically illustrates the latter process disclosed in U.S. Pat. No. 3,689,935. Specifically, an insulating sheet 101 is integrally provided with record signal electrodes 102, 103 on its opposite surfaces, and an ion flow opening 106 extends through the sheet and the electrodes. A source of charged particles 104 such as toner or corona ions is disposed on one side of the opening 106 while a rear electrode 108 is disposed on the other side of the opening, with a record paper 107 having a dielectric record layer being passed between the rear electrode 108 and the record signal electrode 103. It will be seen that lead wires 105a, 105b connect the electrodes 102, 103 with a source of record signal while an ion flow passing through the opening 106 is shown at 109.
In operation, an ion flow from the source 104, which may comprise a Corotron, moves through the opening 106 toward the paper 107. An electric field created by the pair of electrodes 102, 103 may be in the direction to accelerate the passage of ion flow through the opening 106, thus allowing the ions to pass therethrough to produce an electrostatic record on the paper 107. However, when such electric field is in a direction to block the passage of the ion flow, no record is made,
Numerous arrangements are known for providing such an ion flow electrostatic recording. However, all of them share a corona ion generator, a multi-layer record head including electrodes to which a record signal is applied and a dielectric layer which is integral with the electrodes and through which an opening or slit is formed for allowing a selective passage of ions generated, a record medium disposed at a given spacing from the record head, and means for applying a bias voltage between the record medium and the record head.
Preferably, a gap between the record head and the record medium is on the order of 0.2 to 0.5 mm, for example, while a bias voltage on the order of 500 to 1,000 V is applied across the record head and the record medium. If the gap is unstable, a recording response will change, thus causing a variation in the size and the density of dots recorded. If the gap is reduced, the dielectric strength may be insufficient, causing sparks and resulting damage to the record head. If thread-like dust is deposited on the record head, it will extend toward the record medium under the influence of an electric field created, and inject an electric charge onto the record medium from its extremity, causing a black streak to be recorded. Furthermore, as the potential of dots in the resulting latent image rises, the dots recorded may easily increase in diameter.
Where the record medium comprises a drum coated with a dielectric material for repeated use and an electrostatic latent image formed on the drum is developed with a toner and a resulting toner being transferred, the gap between the drum and the record head may be maintained accurately to prevent the occurrence of described difficulties. However, if the record medium comprises a flexible one such as electrostatic recording paper comprising a dielectric record layer applied to a sheet-like conductive base or a base which is treated to be conductive so that the resulting record medium is disposable, it is very difficult to maintain a uniform gap between the record head and the record paper during the running of the latter.
Accordingly, in an electrostatic recording apparatus which utilizes electrostatic recording paper, use is made of a multi-stylus record head. On the other hand, in an electrostatic recording apparatus which utilizes an ion flow electrostatic record head, use is made of a record medium comprising a dielectric record layer formed on a metal drum for repeated use. It would be desirable to provide an electrostatic recording process which enables the use of a combination of an electrostatic record paper and an ion flow electrostatic record head which exhibits excellent recording characteristics. However, such process has not been implemented in the prior art, and its implementation involves a number of difficulties.
In the prior art construction of ion flow recording means, it is necessary to apply a high bias voltage across the electrode 103 and the rear electrode 108 or the dielectric record medium 107 in order to allow the ion flow to image upon the record medium without dispersion in moving from opening 106 to medium 107, and the distance therebetween must be maintained accurately. Deposition of foreign matter around the ion flow opening 106 prevents a normal recording, thus presenting a number of problems, which stand in the way of the implementation of such apparatus.
It is contemplated that such problems of the prior art could be overcome by providing ion flow recording means which performs a recording operation with the ion flow opening and the dielectric record medium disposed in superimposed relationship. This would eliminate an element of instability associated with the maintenance of a constant gap and the need to apply a high voltage which has been used to avoid a dispersion of the ion flow. However, while a mechanism which is used to maintain a constant gap accurately can be dispensed with, such recording means suffers from a disadvantage that a record paper may introduce foreign matter such as dust to plug the ion flow opening or that a running of the record paper may cause an abrasion of the ion flow head.
Another approach to maintain a flexible member in superimposed relationship with a member having an opening in an accurate and positive manner would be to provide a suction box which is partly defined by such member and which is maintained at negative pressure so that a sheet member may be held attracted to the opening. However, such approach results in an inconvenience, when applied to the ion flow recording apparatus, that the ion flow opening will be plugged with foreign matter in a very short time interval and the ion flow head will be abraded by the record paper.